Black porgy larvae were reared from fertilized eggs spawned by one adult reared in the laboratory of Institute of Oceanology, Academia Sinica in May, 1986. The otolith showed a daily growth rhythm under a 12 light - 12 dark photoperiod. The regression equation of chronological age based on the number of daily growth increment, N = D-2.77 was derived, where N is the number of growth increments and D the days after hatching.

The otolith body-diameter length relationship varied significantly between 6L - 6D and 12L - 12D experimental groups. The growth rate of the 12L - 12D group was higher than that of the 6L - 6D group. The mean numbers of growth increments in the otoliths were highly correlated with the frequency of the L, D cycle. Opaque bands formed under 6L - 6D cycles. were poorly etched and easily distinguished (by SEM) from those under l2L - 12D cycles Result of experiments under various light-dark cycles suggested that a 24h light-dark cycle was required for producing daily growth increment. Photoperiod apparently acts as a zeitgeber for the circadian rhythm.